Rechargeable electrochemical elements, in particular lithium cells, in many cases contain a cell stack which is formed from two or more individual cells or individual elements. The individual cells from which such a cell stack is formed are a laminate, which is produced from output conductors, an active electrode film and a separator. Laminates such as these composed of firmly connected individual parts are produced, in particular, as so-called “bicells” with possible sequences comprising a negative electrode/separator/positive electrode/separator/negative electrode or a positive electrode/separator/negative electrode/separator/positive electrode.
A method for producing rechargeable lithium/ion batteries is described in U.S. Pat. No. 5,460,904. In this method, active materials and additives such as, if required, conductivity improvers are mixed in the electrodes or stabilizers in the separator, a specific copolymer, polyvinylidenefluoride hexafluoropropylene (PVDF-HFP), as well as components of a softener, in many cases dibutylphthalate (DBP), after the addition of acetone to dissolve the copolymer, and are drawn out to form a sheet. The electrode sheets and separator sheets are processed in a number of lamination processes to form the above-mentioned bicells. Two or more bicells are formed in layers into a stack which, after insertion into a container composed, for example, of a thermoformed or deep-drawn composite aluminium sheet, filled with electrolyte, sealed with a cover, formation and end closure, are processed to form a complete battery. The electrodes of each polarity are provided with output conductor lugs welded to a collector which is passed through the housing to the exterior. The output conductors are folded closely together to save space and obtain a high energy density in the electrochemical element. It has been found that, in cells such as these, short circuits frequently occur as a result of contact between the output conductor lugs and the metal of the outer composite aluminium sheet.
It would, therefore, be advantageous to improve the resistance of such electro-chemical elements to short circuits.